Pressure-induced contractions in bovine pulmonary artery preparations

Experiments were conducted in a superfusion bioassay system in which the effluent of a bovine main pulmonary artery (generator) was allowed to superfuse a spirally cut precontracted bovine arterial strip (detector), which had been deprived of endothelium. Effluents of endothelium-intact generator relaxed the precontracted detector by an average of 22 +/- 4.1%. Following removal of endothelium of the generator, the relaxing effect of the effluent was only 1%. A rapid increase of transmural pressure in the generator to about 40 mm Hg for 3 min induced contraction of the detector (8.4 +/- 2%) above the histamine-induced tension. In the absence of endothelium, smaller contractions were obtained from the pressurized generator (4.9 +/- 1.8%). This effect was reversible after pressure release. Effluents of endothelium-deprived generator showed no significant vasoactivity. NG-Mono-methyl-L-arginine (L-NMMA, 3.3 x 10(-5) mol/l), a specific inhibitor of nitric oxide (NO), also depressed endothelium-dependent relaxation and caused a 10.5% increase in contraction of the endothelial effluent. When the endothelium-intact generator was exposed to both pressure and L-NMMA, an additive effect was noted. Based on these observations, it was concluded that transient increase of transmural pressure in bovine main pulmonary arteries depresses the endothelium-dependent relaxation and unmasks a small but significant contractile activity of the endothelial effluent.